Apples-to-Apples Compressor Comparison

Wouldn’t it be great if there were a “consumer report” for industrial equipment? Some way to compare various manufacturers rather than relying on anecdotal evidence or personal preference when it’s time to make plant improvements and system upgrades?

Well, almost … there is the Compressed Air and Gas Institute (CAGI). This non-profit organization is made up of competitive equipment manufacturers in the compressed air and gas industry, and is dedicated to educating end-users about efficiently using and applying compressed air. While there are many reputable compressor manufacturers, there are marked differences in compressor performance and manufacturing techniques that can significantly impact day to day operations. Member companies implemented a uniform reporting standard for compressors some years ago, and have now gone one step further by creating an independent performance verification program.

Training materials and educational information are also available from CAGI and the U.S. Department of Energy’s Compressed Air Challenge to assist consumers in making informed and efficient choices in compressed air system selection and design.

What Is a CAGI Data Sheet & How Can I Use It?

CAGI members measure compressors and their productivity based on a standard testing procedure and reporting criteria. These CAGI data sheets are readily available online from most major compressor manufacturer’s websites. End-users then have an “apples to apples” comparison on each compressor’s performance according to CAGI/PNEUROP or ISO standards. It’s a simple, straightforward way to evaluate the total package performance rather that just motor efficiency. (See line-by-line information in Compressed Air Solutions Series for specific line items and explanations.)

Total package performance is key because it is the most accurate accounting of overall compressor performance. It takes into consideration all power consumed compared to all air produced at a certain pressure — including not just the drive motor but fan motors and other components as well.

Members and non-members alike can now participate in CAGI’s Third-Party Testing program. An independent testing laboratory will verify the performance reported on the unit’s CAGI datasheet. Participating manufacturers that pass the verification program test procedures will be allowed to utilize the CAGI Program Verification Seal on the models’ specification sheets and in its product literature. End-users can easily see that the stated air flow capacities and efficiencies have been verified by an independent source.

How Does the Independent Verification Process Work?

The test program administrator will select and test equipment samples on a regular basis to verify that they meet the manufacturers’ certified published performance ratings. Two models will be tested annually per participant.

The administrator will randomly select two units from manufacturer or distributor stock. If the first unit does not pass, the manufacturer has the option to have the second unit tested. If this unit also fails, the manufacturer must re-rate the model based on the test results within 30 days or be ejected from the verification program.

Compare Equipment

It pays to compare when planning a major upgrade or investing in a new air system. The services of a trained compressed air professional who works to understand your facility’s specific operational and application requirements can be invaluable. Consider whether the sales person can clearly explain product features and relate their benefits to your needs. Beware of one-size-fits-all solutions, and evaluate compressor performance among manufacturers.

A collaborative and consultative selling process is more likely to produce an efficient and reliable system, and provide the end-user with maximum return on investment.

CAGI Data Sheets

The Compressed Air and Gas Institute is an organization of competitive companies that manufacture air and gas compressors, pneumatic machinery, as well as air and gas drying and filtration equipment. As a non-profit organization, CAGI seeks to educate end-users and provide helpful, hands-on tools and techniques to improve compressed air system knowledge.

Data Sheets

As a group, these manufacturers developed a standard form for reporting compressor performance. These CAGI data sheets are available from any member. This issue of Compressed Air Solutions offers a line-by-line explanation of these data sheets so that end-users can compare competitive units when making a buying decision.

Water-cooled – No cooling fan power required, but may require cabinet fan.

Oil-injected – Also referred to as fluid injected or fluid cooled.

Oil-free – Yes or no.

Number of stages – Single or multistage.

Line 3: Rated Capacity at Full Load Operating Pressure – The air volume, in CFM, measured at the terminal point of the package, at an agreed-upon set of standard inlet conditions with the compressor operating at the rated pressure (again, measured at the terminal point of the package) stated on Line 4. This takes into account all package air losses and pressure drops.

Line 4: Full Load Operating Pressure – The pressure at the terminal point of the package where the flow and power were measured.

Line 5: Maximum Full Flow Operating Pressure – The maximum pressure at which full flow can be maintained with a given package. It is usually the unload pressure set point for load/unload controls or the pressure at which modulation or other capacity control begins for other control schemes.

Line 6: Drive Motor Nameplate Rating – A nominal horsepower rating applied by the motor manufacturer. This number is not the maximum design capability for the motor. To determine the maximum power output that can be continuously sustained for a motor, multiply the nominal horsepower rating by the service factor. Sustained loads beyond this maximum will shorten the design life of the motor.

Line 7: Drive Motor Nameplate Efficiency – The efficiency of the motor at the nameplate rating.

Line 8: Fan Motor Nameplate Rating (if applicable) – A nominal horsepower rating applied by the motor manufacturer. This applies to all cooler and cabinet fans.

Line 9: Fan Motor Nameplate Efficiency (if applicable) – The efficiency of the motor at the nameplate rating.

Line 10: Total Package Power at Zero Flow – This is input power requirement, in kW, of the total compressor package when the unit is idling. This is the power that the customer will have to provide — and pay for — to operate the compressor even when there is no compressed air being produced.

Line 11: Total Package Power Input at Rated Capacity and Full Load Operating Pressure. This is the complete input power requirement, in kW, of the compressor package when the compressor is running at the rated capacity listed in Line 3 and the full load operating pressure listed in Line 4. This is the power that the customer will have to provide — and pay for — to operate the compressor package at the rated capacity and flow. It includes all efficiency, power factor and accessory losses. When comparing these numbers between manufacturers, it is important to make certain that power consumption of the remote cooler packages is included. Some manufacturers may not count remote cooling packages in this number. This may include remote-mounted air-cooled coolers and closed-loop water-cooling systems. Also, power should be measured on the supply side of remote-mounted variable-frequency drive controls.

Line 12: Specific Package Input Power at Rated Capacity and Full Load Operating Pressure Package Input Power is the measure of how efficiently a compressor package produces compressed air. It is the power input divided by the flow in units of 100 CFM. A 563-CFM machine that requires 91.58 kW at the rated pressure would have a specific power of 16.3 (91.58/5.63 = 16.3). Comparing specific power ratings allows users to determine which compressor delivers air at the lowest cost per CFM.